Composite materials in which load bearing fibres are embedded within a polymeric matrix material are commonly used for high performance structural applications.
In such a composite material, the fibres carry the majority of the applied load and therefore a good design aligns the fibres of the composite with the load path through the component. In reality, there are often multiple load paths and therefore the fibres must be oriented in multiple directions. Therefore a fibre lay-up may have a majority of fibre plies oriented in a primary direction, with additional plies oriented at other angles, say 30° or 45°, to the primary direction. If a component experiences a range of different load paths, or if the load paths are unknown, the lay-up of the composite may comprise a number of 0, 90°+45° and −45° angled plies which allow the composite to withstand load paths in any direction.
The fibre lay-up of the composite material may be carried out manually or by an automated process. Manual fibre lay-up is simple and cost effective for smaller part quantities. However it is slow and requires a skilled operator in order to ensure that each fibre ply is correctly placed onto the shaped former or mould.
Alternatively an automated process may be used to construct the fibre lay-up. In such a process, a fibre or tape laying machine can be used to place layers of composite fibre onto the shaped former in different orientations to construct the part.
Automated fibre or tape lay-up can be readily applied, using a range of tape widths, to surfaces having simple curvatures. However for surfaces having more complex curvatures, it becomes necessary to limit the width of the tape laid by the machine in order to ensure correct fibre placement on the shaped former. For highly complex curvatures, it becomes necessary to limit automated lay-up techniques to use with fibre tows in order to be able to steer the fibre over the highly curved surfaces.
While lay-up using a single tow placement machine over a complex former geometry is easier, the fibre lay-up rates are usually very much lower than for tape laying. To overcome this multiple tow placement heads have been developed which makes the machine more complicated and also decreases the amount of control that a user has over the tows during the lay-up process. This in turn can result in defects such as gaps and overlaps being generated during the lay-up process which becomes a significant concern when making high performance parts without incurring a weight penalty.
Due to the limitations of an automated single tow placement machine, the design of the composite component, and specifically the fibre path definitions, becomes more complex and time-consuming. In addition, the complex curvatures of the shaped former makes the repeatability of the tow path placement more difficult because the machine has limited control over the tows between the cutting step and before they are laid down. This necessitates a higher specification, and therefore more costly, machine.
Furthermore, manufacturing induced defects in the composite parts become unavoidable which requires a higher safety factor. This results in an increase in the weight of the part and makes its manufacture more costly.